File: simpleeval.py

package info (click to toggle)
simpleeval 0.9.10-1
  • links: PTS, VCS
  • area: main
  • in suites: bullseye, sid
  • size: 160 kB
  • sloc: python: 1,025; makefile: 27; sh: 9
file content (609 lines) | stat: -rw-r--r-- 20,550 bytes parent folder | download
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
"""
SimpleEval - (C) 2013-2019 Daniel Fairhead
-------------------------------------

An short, easy to use, safe and reasonably extensible expression evaluator.
Designed for things like in a website where you want to allow the user to
generate a string, or a number from some other input, without allowing full
eval() or other unsafe or needlessly complex linguistics.

-------------------------------------

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

-------------------------------------

Initial idea copied from J.F. Sebastian on Stack Overflow
( http://stackoverflow.com/a/9558001/1973500 ) with
modifications and many improvements.

-------------------------------------
Contributors:
- corro (Robin Baumgartner) (py3k)
- dratchkov (David R) (nested dicts)
- marky1991 (Mark Young) (slicing)
- T045T (Nils Berg) (!=, py3kstr, obj.
- perkinslr (Logan Perkins) (.__globals__ or .func_ breakouts)
- impala2 (Kirill Stepanov) (massive _eval refactor)
- gk (ugik) (Other iterables than str can DOS too, and can be made)
- daveisfera (Dave Johansen) 'not' Boolean op, Pycharm, pep8, various other fixes
- xaled (Khalid Grandi) method chaining correctly, double-eval bugfix.
- EdwardBetts (Edward Betts) spelling correction.
- charlax (Charles-Axel Dein charlax) Makefile and cleanups
- mommothazaz123 (Andrew Zhu) f"string" support, Python 3.8 support
- lubieowoce (Uryga) various potential vulnerabilities
- JCavallo (Jean Cavallo) names dict shouldn't be modified
- Birne94 (Daniel Birnstiel) for fixing leaking generators.
- patricksurry (Patrick Surry) or should return last value, even if falsy.

-------------------------------------
Basic Usage:

>>> s = SimpleEval()
>>> s.eval("20 + 30")
50

You can add your own functions easily too:

if file.txt contents is "11"

>>> def get_file():
...     with open("file.txt", 'r') as f:
...         return f.read()

>>> s.functions["get_file"] = get_file
>>> s.eval("int(get_file()) + 31")
42

For more information, see the full package documentation on pypi, or the github
repo.

-----------

If you don't need to re-use the evaluator (with it's names, functions, etc),
then you can use the simple_eval() function:

>>> simple_eval("21 + 19")
40

You can pass names, operators and functions to the simple_eval function as
well:

>>> simple_eval("40 + two", names={"two": 2})
42

"""

import ast
import operator as op
import sys
from random import random

PYTHON3 = sys.version_info[0] == 3

########################################
# Module wide 'globals'

MAX_STRING_LENGTH = 100000
MAX_COMPREHENSION_LENGTH = 10000
MAX_POWER = 4000000  # highest exponent
DISALLOW_PREFIXES = ['_', 'func_']
DISALLOW_METHODS = ['format', 'format_map', 'mro']

# Disallow functions:
# This, strictly speaking, is not necessary.  These /should/ never be accessable anyway,
# if DISALLOW_PREFIXES and DISALLOW_METHODS are all right.  This is here to try and help
# people not be stupid.  Allowing these functions opens up all sorts of holes - if any of
# their functionality is required, then please wrap them up in a safe container.  And think
# very hard about it first.  And don't say I didn't warn you.

DISALLOW_FUNCTIONS = {type, isinstance, eval, getattr, setattr, help, repr, compile, open}

if PYTHON3:
    exec('DISALLOW_FUNCTIONS.add(exec)') # exec is not a function in Python2...


########################################
# Exceptions:


class InvalidExpression(Exception):
    """ Generic Exception """

    pass


class FunctionNotDefined(InvalidExpression):
    """ sorry! That function isn't defined! """

    def __init__(self, func_name, expression):
        self.message = "Function '{0}' not defined," \
                       " for expression '{1}'.".format(func_name, expression)
        setattr(self, 'func_name', func_name)  # bypass 2to3 confusion.
        self.expression = expression

        # pylint: disable=bad-super-call
        super(InvalidExpression, self).__init__(self.message)


class NameNotDefined(InvalidExpression):
    """ a name isn't defined. """

    def __init__(self, name, expression):
        self.name = name
        self.message = "'{0}' is not defined for expression '{1}'".format(
            name, expression)
        self.expression = expression

        # pylint: disable=bad-super-call
        super(InvalidExpression, self).__init__(self.message)


class AttributeDoesNotExist(InvalidExpression):
    """attribute does not exist"""

    def __init__(self, attr, expression):
        self.message = \
            "Attribute '{0}' does not exist in expression '{1}'".format(
                attr, expression)
        self.attr = attr
        self.expression = expression


class FeatureNotAvailable(InvalidExpression):
    """ What you're trying to do is not allowed. """

    pass


class NumberTooHigh(InvalidExpression):
    """ Sorry! That number is too high. I don't want to spend the
        next 10 years evaluating this expression! """

    pass


class IterableTooLong(InvalidExpression):
    """ That iterable is **way** too long, baby. """

    pass


########################################
# Default simple functions to include:


def random_int(top):
    """ return a random int below <top> """

    return int(random() * top)


def safe_power(a, b):  # pylint: disable=invalid-name
    """ a limited exponent/to-the-power-of function, for safety reasons """

    if abs(a) > MAX_POWER or abs(b) > MAX_POWER:
        raise NumberTooHigh("Sorry! I don't want to evaluate {0} ** {1}"
                            .format(a, b))
    return a ** b


def safe_mult(a, b):  # pylint: disable=invalid-name
    """ limit the number of times an iterable can be repeated... """

    if hasattr(a, '__len__') and b * len(a) > MAX_STRING_LENGTH:
        raise IterableTooLong('Sorry, I will not evalute something that long.')
    if hasattr(b, '__len__') and a * len(b) > MAX_STRING_LENGTH:
        raise IterableTooLong('Sorry, I will not evalute something that long.')

    return a * b


def safe_add(a, b):  # pylint: disable=invalid-name
    """ iterable length limit again """

    if hasattr(a, '__len__') and hasattr(b, '__len__'):
        if len(a) + len(b) > MAX_STRING_LENGTH:
            raise IterableTooLong("Sorry, adding those two together would"
                                  " make something too long.")
    return a + b


########################################
# Defaults for the evaluator:

DEFAULT_OPERATORS = {ast.Add: safe_add, ast.Sub: op.sub, ast.Mult: safe_mult,
                     ast.Div: op.truediv, ast.FloorDiv: op.floordiv,
                     ast.Pow: safe_power, ast.Mod: op.mod,
                     ast.Eq: op.eq, ast.NotEq: op.ne,
                     ast.Gt: op.gt, ast.Lt: op.lt,
                     ast.GtE: op.ge, ast.LtE: op.le,
                     ast.Not: op.not_,
                     ast.USub: op.neg, ast.UAdd: op.pos,
                     ast.In: lambda x, y: op.contains(y, x),
                     ast.NotIn: lambda x, y: not op.contains(y, x),
                     ast.Is: lambda x, y: x is y,
                     ast.IsNot: lambda x, y: x is not y,
                     }

DEFAULT_FUNCTIONS = {"rand": random, "randint": random_int,
                     "int": int, "float": float,
                     "str": str if PYTHON3 else unicode}

DEFAULT_NAMES = {"True": True, "False": False, "None": None}

ATTR_INDEX_FALLBACK = True


########################################
# And the actual evaluator:


class SimpleEval(object):  # pylint: disable=too-few-public-methods
    """ A very simple expression parser.
        >>> s = SimpleEval()
        >>> s.eval("20 + 30 - ( 10 * 5)")
        0
        """
    expr = ""

    def __init__(self, operators=None, functions=None, names=None):
        """
            Create the evaluator instance.  Set up valid operators (+,-, etc)
            functions (add, random, get_val, whatever) and names. """

        if not operators:
            operators = DEFAULT_OPERATORS.copy()
        if not functions:
            functions = DEFAULT_FUNCTIONS.copy()
        if not names:
            names = DEFAULT_NAMES.copy()

        self.operators = operators
        self.functions = functions
        self.names = names

        self.nodes = {
            ast.Num: self._eval_num,
            ast.Str: self._eval_str,
            ast.Name: self._eval_name,
            ast.UnaryOp: self._eval_unaryop,
            ast.BinOp: self._eval_binop,
            ast.BoolOp: self._eval_boolop,
            ast.Compare: self._eval_compare,
            ast.IfExp: self._eval_ifexp,
            ast.Call: self._eval_call,
            ast.keyword: self._eval_keyword,
            ast.Subscript: self._eval_subscript,
            ast.Attribute: self._eval_attribute,
            ast.Index: self._eval_index,
            ast.Slice: self._eval_slice,
        }

        # py3k stuff:
        if hasattr(ast, 'NameConstant'):
            self.nodes[ast.NameConstant] = self._eval_constant

        # py3.6, f-strings
        if hasattr(ast, 'JoinedStr'):
            self.nodes[ast.JoinedStr] = self._eval_joinedstr  # f-string
            self.nodes[ast.FormattedValue] = self._eval_formattedvalue  # formatted value in f-string

        # py3.8 uses ast.Constant instead of ast.Num, ast.Str, ast.NameConstant
        if hasattr(ast, 'Constant'):
            self.nodes[ast.Constant] = self._eval_constant

        # Defaults:

        self.ATTR_INDEX_FALLBACK = ATTR_INDEX_FALLBACK
        
        # Check for forbidden functions:

        for f in self.functions.values():
            if f in DISALLOW_FUNCTIONS:
                raise FeatureNotAvailable('This function {} is a really bad idea.'.format(f))


    def eval(self, expr):
        """ evaluate an expresssion, using the operators, functions and
            names previously set up. """

        # set a copy of the expression aside, so we can give nice errors...

        self.expr = expr

        # and evaluate:
        return self._eval(ast.parse(expr.strip()).body[0].value)

    def _eval(self, node):
        """ The internal evaluator used on each node in the parsed tree. """

        try:
            handler = self.nodes[type(node)]
        except KeyError:
            raise FeatureNotAvailable("Sorry, {0} is not available in this "
                                      "evaluator".format(type(node).__name__))

        return handler(node)

    @staticmethod
    def _eval_num(node):
        return node.n

    @staticmethod
    def _eval_str(node):
        if len(node.s) > MAX_STRING_LENGTH:
            raise IterableTooLong("String Literal in statement is too long!"
                                  " ({0}, when {1} is max)".format(
                                      len(node.s), MAX_STRING_LENGTH))
        return node.s

    @staticmethod
    def _eval_constant(node):
        if hasattr(node.value, '__len__') and len(node.value) > MAX_STRING_LENGTH:
            raise IterableTooLong("Literal in statement is too long!"
                                  " ({0}, when {1} is max)".format(len(node.value), MAX_STRING_LENGTH))
        return node.value

    def _eval_unaryop(self, node):
        return self.operators[type(node.op)](self._eval(node.operand))

    def _eval_binop(self, node):
        return self.operators[type(node.op)](self._eval(node.left),
                                             self._eval(node.right))

    def _eval_boolop(self, node):
        if isinstance(node.op, ast.And):
            vout = False
            for value in node.values:
                vout = self._eval(value)
                if not vout:
                    return vout
            return vout
        elif isinstance(node.op, ast.Or):
            for value in node.values:
                vout = self._eval(value)
                if vout:
                    return vout
            return vout

    def _eval_compare(self, node):
        right = self._eval(node.left)
        to_return = True
        for operation, comp in zip(node.ops, node.comparators):
            if not to_return:
                break
            left = right
            right = self._eval(comp)
            to_return = self.operators[type(operation)](left, right)
        return to_return

    def _eval_ifexp(self, node):
        return self._eval(node.body) if self._eval(node.test) \
                                         else self._eval(node.orelse)

    def _eval_call(self, node):
        if isinstance(node.func, ast.Attribute):
            func = self._eval(node.func)
        else:
            try:
                func = self.functions[node.func.id]
            except KeyError:
                raise FunctionNotDefined(node.func.id, self.expr)
            except AttributeError as e:
                raise FeatureNotAvailable('Lambda Functions not implemented')

            if func in DISALLOW_FUNCTIONS:
                raise FeatureNotAvailable('This function is forbidden')

        return func(
            *(self._eval(a) for a in node.args),
            **dict(self._eval(k) for k in node.keywords)
        )

    def _eval_keyword(self, node):
        return node.arg, self._eval(node.value)

    def _eval_name(self, node):
        try:
            # This happens at least for slicing
            # This is a safe thing to do because it is impossible
            # that there is a true exression assigning to none
            # (the compiler rejects it, so you can't even
            # pass that to ast.parse)
            if hasattr(self.names, '__getitem__'):
                return self.names[node.id]
            elif callable(self.names):
                return self.names(node)
            else:
                raise InvalidExpression('Trying to use name (variable) "{0}"'
                                        ' when no "names" defined for'
                                        ' evaluator'.format(node.id))

        except KeyError:
            if node.id in self.functions:
                return self.functions[node.id]

            raise NameNotDefined(node.id, self.expr)

    def _eval_subscript(self, node):
        container = self._eval(node.value)
        key = self._eval(node.slice)
        try:
            return container[key]
        except KeyError:
            raise

    def _eval_attribute(self, node):
        for prefix in DISALLOW_PREFIXES:
            if node.attr.startswith(prefix):
                raise FeatureNotAvailable(
                    "Sorry, access to __attributes "
                    " or func_ attributes is not available. "
                    "({0})".format(node.attr))
        if node.attr in DISALLOW_METHODS:
            raise FeatureNotAvailable(
                "Sorry, this method is not available. "
                "({0})".format(node.attr))
        # eval node
        node_evaluated = self._eval(node.value)

        # Maybe the base object is an actual object, not just a dict
        try:
            return getattr(node_evaluated, node.attr)
        except (AttributeError, TypeError):
            pass

        # TODO: is this a good idea?  Try and look for [x] if .x doesn't work?
        if self.ATTR_INDEX_FALLBACK:
            try:
                return node_evaluated[node.attr]
            except (KeyError, TypeError):
                pass

        # If it is neither, raise an exception
        raise AttributeDoesNotExist(node.attr, self.expr)

    def _eval_index(self, node):
        return self._eval(node.value)

    def _eval_slice(self, node):
        lower = upper = step = None
        if node.lower is not None:
            lower = self._eval(node.lower)
        if node.upper is not None:
            upper = self._eval(node.upper)
        if node.step is not None:
            step = self._eval(node.step)
        return slice(lower, upper, step)

    def _eval_joinedstr(self, node):
        length = 0
        evaluated_values = []
        for n in node.values:
            val = str(self._eval(n))
            if len(val) + length > MAX_STRING_LENGTH:
                raise IterableTooLong("Sorry, I will not evaluate something this long.")
            evaluated_values.append(val)
        return ''.join(evaluated_values)

    def _eval_formattedvalue(self, node):
        if node.format_spec:
            fmt = "{:" + self._eval(node.format_spec) + "}"
            return fmt.format(self._eval(node.value))
        return self._eval(node.value)


class EvalWithCompoundTypes(SimpleEval):
    """
        SimpleEval with additional Compound Types, and their respective
        function editions. (list, tuple, dict, set).
    """

    def __init__(self, operators=None, functions=None, names=None):
        super(EvalWithCompoundTypes, self).__init__(operators, functions, names)

        self.functions.update(
            list=list,
            tuple=tuple,
            dict=dict,
            set=set)

        self.nodes.update({
            ast.Dict: self._eval_dict,
            ast.Tuple: self._eval_tuple,
            ast.List: self._eval_list,
            ast.Set: self._eval_set,
            ast.ListComp: self._eval_comprehension,
            ast.GeneratorExp: self._eval_comprehension,
        })

    def eval(self, expr):
        self._max_count = 0
        return super(EvalWithCompoundTypes, self).eval(expr)

    def _eval_dict(self, node):
        return {self._eval(k): self._eval(v)
                for (k, v) in zip(node.keys, node.values)}

    def _eval_tuple(self, node):
        return tuple(self._eval(x) for x in node.elts)

    def _eval_list(self, node):
        return list(self._eval(x) for x in node.elts)

    def _eval_set(self, node):
        return set(self._eval(x) for x in node.elts)

    def _eval_comprehension(self, node):
        to_return = []

        extra_names = {}

        previous_name_evaller = self.nodes[ast.Name]

        def eval_names_extra(node):
            """
                Here we hide our extra scope for within this comprehension
            """
            if node.id in extra_names:
                return extra_names[node.id]
            return previous_name_evaller(node)

        self.nodes.update({ast.Name: eval_names_extra})

        def recurse_targets(target, value):
            """
                Recursively (enter, (into, (nested, name), unpacking)) = \
                             and, (assign, (values, to), each
            """
            if isinstance(target, ast.Name):
                extra_names[target.id] = value
            else:
                for t, v in zip(target.elts, value):
                    recurse_targets(t, v)

        def do_generator(gi=0):
            g = node.generators[gi]
            for i in self._eval(g.iter):
                self._max_count += 1

                if self._max_count > MAX_COMPREHENSION_LENGTH:
                    raise IterableTooLong('Comprehension generates too many elements')
                recurse_targets(g.target, i)
                if all(self._eval(iff) for iff in g.ifs):
                    if len(node.generators) > gi + 1:
                        do_generator(gi+1)
                    else:
                        to_return.append(self._eval(node.elt))

        try:
            do_generator()
        finally:
            self.nodes.update({ast.Name: previous_name_evaller})

        return to_return


def simple_eval(expr, operators=None, functions=None, names=None):
    """ Simply evaluate an expresssion """
    s = SimpleEval(operators=operators,
                   functions=functions,
                   names=names)
    return s.eval(expr)